Doctor Who showrunner Steven Moffat has confirmed that the Doctor's arch-enemies, the Daleks, won't be showing up again any time soon. He told BBC News:

They aren't going to make an appearance for a while. We thought it was about time to give them a rest... There's a problem with the Daleks. They are the most famous of the Doctor's adversaries and the most frequent, which means they are the most reliably defeatable enemies in the universe.

He added that the Doctor has defeated the Daleks "about 400 times." [BBC News]